Tabulating the Rabbit Hole

Last week's post, Mapping the Rabbit Hole, ended with an action:-

It's time to wrap up the series on early 19th century chess periodicals. It began with '2019-02-14: Down the Rabbit Hole • Google Books' [...] The next step, which shouldn't take much time, will be to catalog the various periodicals by year.

The following chart shows periodicals published by country and by year.

Creating that chart didn't take much time, but interpreting it is another matter. I count 25 intersections of year and country with more than a single periodical. Looking into those will take time. For starters, here are two intersections with more than two periodicals:-

1861 - UK: 3
1868 - FR: 5

The first is 'The Chess Player's Chronicle' (1861); the second is 'Le Philidorien' (1868). A quick look at the Google scans established that these are indeed duplicate copies, but I couldn't decide which versions should be used in the future.